There are many operating systems (particularly the Linux based ones) being offered for free in form of ISO image downloads. Typically, you would download these ISO image files to your PC and then either burn them on to a blank CD/DVD (whichever is suitable for the ISO file size) or create a bootable USB flash disk using the ISO image. There are many tools for both of these tasks. For example, ImgBurn can be used to burn the ISO image files on the blank optical media, while Rufus or Unetbootin can be used to create bootable USB flash disks.
But when you do not have any space USB flash disk, a blank CD/DVD, or even access to run these tools on a PC, then you are pretty much helpless. Fortunately, if you have a Android phone with considerable amount of storage space, then you use it to boot almost any type of bootable ISO image including all the popular Linux distributions and the Windows ISO images. This is possible through an Android app called DriveDroid.
DriveDroid app requires a rooted phone to work. If your phone is not rooted, then you can try Root Genius to get root access in it. Once installed, DriveDroid will ask you for the root access after which you can proceed and download one of the Linux ISO images from withing the DriveDroid app. However, if you have already downloaded any bootable ISO image, then you can copy them to the Downloads\Images folder on your SDCard. This is the default folder where ISO images are kept.
After an image is downloaded, it will be listed in the DriveDroid interface. You can tap on it to view various hosting options for it – mount it as writable USB disk, mount it as read/write USB disk, or mount it as a CD-ROM disk. You can change various options related to USB mounting and the ISO images folder in the DriveDroid settings.
Now, connect your Android phone to your PC and press the power button on the PC. During the booting process, press F12 to pull up the boots election menu and choose your Android device from the menu. Pretty soon, you would be booting from the ISO image located on your Android phone. You can still use the Android phone and your PC simultaneously without any problems.
This way, you can launch and run any Linux distribution right from your Android phone. You can also use this method for installing Windows 10 on your PC. However, for better performance, it is recommended that you have a class 10 micro SD card in your phone.
You can download DriveDroid app from https://play.google.com/store/apps/details?id=com.softwarebakery.drivedroid.